Multiphase power supply technology is widely used in applications that output high current. Normally, the phases of an N-phase multiphase configuration operate such that the phases are shifted by 2π/N [rad] relative to each other. Hence, an N-phase multiphase power supply circuit in which the switch frequency for each phase is fs performs the same operation as a single-phase power supply with a switch frequency of Nfs. Therefore, there are advantages such as an improvement in response speed to load change and a reduction in ripple amplitude. On the other hand, the major drawback is the influence caused by mismatch.
Normally, in the case of an ideal N-phase multiphase DC-DC converter, as the frequency characteristics of an output signal, a spurious component is observed in Nfs frequency component and waves of the Nfs frequency component. That is, an fs component which is a switch frequency for each phase is cancelled out when adding currents for each phase and thus the spurious component is not observed in an output voltage.
However, in a realistic multiphase power supply, there is a mismatch of the order of up to 20% between inductance values for the respective phases. Due to this influence, an fs component is not cancelled out when adding currents for each phase, and thus, the fs component remains in an output signal. In addition, since this low-frequency component is less likely to be influenced by an LC low-pass filter at a subsequent stage, strong spurious components are observed.
A technique for solving this problem is conventionally presented. The technique is such that an inductance for each phase is measured in advance, and two phases whose inductance values are close to each other are rearranged in a reverse phase relationship. Specifically, when the inductance values for two phases are the same or close to each other and are different from the inductance values for the other phases, the configuration is arranged such that these two phases have the reverse phase relationship. By this, the phases shifted by 180 degrees cancel each other out (the ripple for the phases on opposite sides is canceled out), reducing an fs component in an output voltage. By this, an fs component in an output signal can be reduced. This method, however, has a problem that the fs component cannot be sufficiently removed, depending on the difference in inductance value between the two phases (the amount of mismatch). In addition, there is another problem that when only the inductance value for one phase is different from the inductance values for the other phases, an effect cannot be obtained.
As such, the above-described conventional art proposes a technique for solving the problem that a spurious low-frequency component is observed in an output signal. However, there are many cases in which an fs component cannot be sufficiently removed, depending on the amount of mismatch. In addition, there is a problem that an effect is not brought about when only the inductance for one phase is different from the inductance values for the other phases.